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96
CHEMICAL ENGINEERING
Advisable speed of conveyor (Table 9) ................   175 ft         minute
Minimum capacity of horizontal conveyor (120,000/800)  150 tons per hour Required minimum due to inclination (150/0.97) ......   155 tons per hour
Assume spacing of flights as 18 in., and weight of sand and gravel at ..................................... 110 lb   per  cubic foot
W   -I™-   °-°028 X175 X 110 X A                   ^         .    ,   .
wh — 15U --- ~ - -                   Formula (11)
A = 50 sq. in. + 6 per cent for inclination = 53 sq. in.
Take A = 60 for safety and flights 5 X 12 in. Power requirements:
Horsepower -
Hon.power
Costs: RCf.
0.988 X 1M X MO + 1«0 X 5.25
Formula (12)
1.5V60
___
(0.0115 X 60 + 0.0516 X A/60 + 7)100 1,441.63— say 1,450, for shoe jflights (0.0115 X 60 + 0.0516 X A/60 + 7)100 + 3.0 VoO 1,153.25— say 1,465, for roller flights
Formula (1 3)
#/->/« - ((0.00323 X 60 + 0.00237V60 + 1.075)100 + 0.6\/60)1-50
200.05— say 200.                                                       Formula (14)
Take* market price at 25 per cent above relative costs. Ocwt « 1.25 X 1,450 = 1,812.50— say $1,815.00— shoe flights *= 1.25 X 1,465 = 1,831.25— say $1,835.00— roller flights.
SHOE FLIGHTS charges :      (0 . 085 X 1,815) ...........      $154 . 28
(0.085 X 1,835) .................
Labor charge:       (0 . 03 X 12)800 ............         288 . 00
Supply oxpciiHc:   (0.03 X 18)800 ...........        432.00
Powc»r charge : I )(»pr«wiat,ion :
(0.03 X 18)800 (0.02X18)800 (0 . 03 X 18)800 (0.03 X 15)800 (1 . 25 X 200) charge: (0.20 X 1,815) (0.20X1,835)
432 . 00
250 . 00 363.00
ROLI/EITI FLIGHTS
$155.98
288 . 00
288.00
360.00 250 . 00
367.00
$1,919.28            $1,708.98
Net Operating Cost:
(1 ,919.28/120,000)............SO.016     per ton—shoe flights.
C1 ,70S.98/120,000)............$0.01424 per ton—roller flights.
Screw conveyors are helical flights wound about a central shaft (screws) n'volvinfc in troughs or boxes through which the load is pushed by the screw. The size; of the conveyor is designated by the diameter of the screw, but the diaitiHer of the trough may vary between wide limits, from one which is only Lsightly larger than the screw to a commodious box encasing the screw in which the material handled collects and the screw makes its own trough in a bed of material.